Abstract
Extreme ultraviolet (XUV) and X-ray free-electron lasers enable new scientific opportunities. Their ultra-intense coherent femtosecond pulses give unprecedented access to the structure of undepositable nanoscale objects and to transient states of highly excited matter. In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose end-station CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments. XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units. Procedures to establish temporal and spatial overlap of the two pulses in CAMP are presented, with emphasis on the optimization of the spatial overlap at long time-delays via time-dependent features, for example in ion spectra of atomic clusters.
Highlights
Ultra-bright extreme ultraviolet (XUV) and X-ray pulses of free-electron lasers (FELs) efficiently ionize atoms (Sorokin et al, 2007) and turn condensed matter into highly excited plasma states if focused to a small spot (Wabnitz et al, 2002; Chapman et al, 2007)
In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose endstation CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments
XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units
Summary
Ultra-bright extreme ultraviolet (XUV) and X-ray pulses of free-electron lasers (FELs) efficiently ionize atoms (Sorokin et al, 2007) and turn condensed matter into highly excited plasma states if focused to a small spot (Wabnitz et al, 2002; Chapman et al, 2007). The complex and intertwined dynamics of electrons and ions proceed on various timescales from the femtosecond to the nanosecond regime, as, for example, indicated by studies on atomic clusters (Ferguson et al, 2016; Gorkhover et al, 2016; Schutte et al, 2015; Fluckiger et al, 2016). The CAMP instrument (Struder et al, 2010), which has been very successful in the first few years at the X-ray FEL LCLS (Bostedt et al, 2016), was recently installed as a permanent end-station at beamline BL1 (Erk et al, 2018) of the FLASH FEL in Hamburg (Ackermann et al, 2007; Feldhaus, 2010). In order to investigate the complex FEL-induced dynamics on femtosecond to nanosecond time-scales with a second FEL pulse, the split-and-delay unit DESC was designed and integrated into the BL1 beamline in front of the CAMP end-station. Time-resolved ion spectra of atomic clusters are used to illustrate the optimization procedure for long timedelays
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